oasis: Add library paths required on Debian

This path is needed on Debian, where the Xen libraries are
installed in a non-standard path.   It should not do any
harm on CentOS as it is an addition to the library search
path, not a replacement.    Ideally the configure script
would fill the path in as appropriate.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge branch 'debian' of git://github.com/euanh/ocaml-xen-lowlevel-libs into merge-euan

Signed-off-by: David Scott <dave.scott@eu.citrix.com>

Conflicts:
	setup.ml

OASIS needed to be regenerated.
Merge pull request #35 from djs55/merge-euan

Merge Euan's fix for debian, regenerate OASIS